High energy liquid fluoroaminomethane storable high energy oxidizer and method of propulsion



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HIGH ENERGY LIQU'fD FLOUROAMINOMETHANE STORABLE OXIDIZER AND METHOD OF PROPULSION Fued June 25, 1963 l l l I I I Tern peroture x I0 VAPOR PRESSURE OF DINITROGEN TETRAOXIDE AND TRIS (D IFLUOROAMINO) FLUOROMETHANE wanerw whoflon Barry D'.Allan,

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3,534,554 HIGH ENERGY LIQUID FLUOROAMINO- METHANE STORABLE HIGH ENERGY OX- IDIZER AND METHOD OF PROPULSION Barry D. Allan and Walter W. Wharton, Huntsville, Ala., assignors to the United States of America as represented by the Secretary of the Army Filed June 25, 1963, Ser. No. 290,903 Int. Cl. (306d /08; F231 1/02 U.S. Cl. 60214 11 Claims The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to high energy oxidizers and a method for using the oxidizers. More particularly the invention relates to high energy liquid oxidizers for use as propellants in reaction motors and to a method of operating a bipropellant reaction motor utilizing these oxidizers.

One problem which limits the application of many high energy propellants to military use in rocket motors is the difficulty in storing these propellants. A bipropellant system based on the use of liquid hydrogen and liquid oxygen, for example, offers considerable advantage in terms of thrust over many other liquid systems now in use. However, because of the extreme requirements for storing and handling liquid hydrogen and liquid oxygen, these propellants are not generally suitable for use in military rockets. One characteristic of a liquid propellant which is necessary for it to be acceptable for military use, particularly land armies, is that storage of the propellant must not require extreme temperature control. Maintenance of extremely cold storage conditions requires heavy, bulky quipment that cannot be tolerated in resent day military missile systems which must be maneuverable.

It has now been determined that a high energy oxidizer consisting essentially of a solution of tris(difluoroamino) fiuoromethane and dinitrogen tetraoxide greatly increases the specific impulse when employed with conventional fuels while at the same time being readily storeable. Furthermore, the oxidizer offers the advantage of being hypergolic with many fuels normally used in rocket motors. Moreover, the oxidizer solution is less sensitive to temperature changes and mechanical shock than is the pure tris(difluoroamino)fluoromethane.

In accordance with the foregoing, it is an object of the invention to provide high energy oxidizers for use as propellants in reaction motors.

A further object of the present invention is to provide high energy oxidizers which are readily storeable.

A still further object of the invention is to provide storeable, high energy oxidizers which are hypergolic with many fuels used in reaction motors.

Another object of the invention is to provide high energy liquid oxidizer solutions containing tris(difluoroamino)fluoromethane which are less sensitive to mechanical shock and temperature change than the pure tris(difluoroamino)fiuoromethane.

As additional object of the present invention is to provide a method for operating liquid bipropellant reaction motors by introducing into the combustion chamber of a reaction motor one or more of the high energy oxidizers of the invention and a fuel hypergolic with the oxidizer.

The manner in which these and other objects may be accomplished will become apparent from the detailed description presented hereinbelow.

The figure shown is a graph illustrating the vapor pressure curves of dinitrogen tetraoxide and tris(difluoroamino)fluoromethane.

3,534,554 Patented Oct. 20, 1970 Dinitrogen tetraoxide is a commercially available liquid having a boiling point of 213 C. at a pressure of 760 millimeters of mercury. In the liquid state, dinitrogen tetraoxide partially dissociates forming nitrogen dioxide, N0 which gives the liquid a brown color. The extent of dissociation depends upon the temperature of the liquid with an increase in temperature bringing an increase in dissociation. In regards to the present invention, it is to be understood that when reference is made to dinitrogen tetraoxide it is intended to include dinitrogen tetraoxide in equilibrium with nitrogen dioxide, the only manner in which dinitrogen tetraoxide exists as a liquid.

The oxidizer compositions of the invention can be utilized at temperatures of 60 F. if nitric oxide is added to the liquid dinitrogen tetraoxide. Generally, nitric oxide will be incorporated into the compositions in an amount of 5% to 15% by weight based on the weight of dinitrogen tetraoxide. If desired, the compositions can always contain nitric oxide since it does not interfere with their use as oxidizers.

Tris(difluoroamino)fluoromethane, CF(NF has one of the highest content of NF bonds per carbon atom of any presently known compound. The relatively weak fluorine to nitrogen bond makes the fluorine readily available as an oxidizer. The compound is synthesized by fluorinating ammeline. There are many established fluorination procedures that are well known in the art which can be used to prepare the tris(difluoroamino )fluoromethane. One such method, the static-bed method, is as follows:

One and one-half grams of dry ammeline is placed in a metal boat and a gas stream consisting of fluorine diluted with nitrogen (5.5% by volume of gas stream being fluorine) is passed over the ammeline at about 5 C. for seven hours at which time .13 mole of fluorine has been used. The exit gas is passed through a sodium fluoride scrubber at C. to remove hydrogen fluoride. The eflluent gases are collected in a cold trap at a temperature of 78 C. The contents of the trap are allowed to warm to 20 C. to drive off all highly volatile materials. The remaining liquid material contains the tris(difluoroamin0) fiuoromethane which is recovered by normal vacuum distillation procedures. The boiling point of the desired product at various pressures are shown in the figure. The yield is greater than 3 Tris(difluoroamino)fiuoromethane is theoretically an excellent oxidizer. However, it has been difficult to make use of its potential due to its sensitivity to temperature changes. Detonations have frequently occurred when tris (difluoroamino)fiuoromethane was cycled between room temperature and the temperature of liquid nitrogen.

Another factor to be considered in the use of tris(difluoroamino)fiuoromethane is its boiling point of between 8 and 9 C. While such a boiling point places the compound within the class of storeable propellants, any increase in its boiling point obviously facilitates storage.

It has now been determined that compositions consisting essentially of 20% to 80% by weight tris(difluoroamino)fluoromethane with the remainder of the compositions being dinitrogen tetraoxide are excellent oxidizers for use in reaction motors. Particularly, those compositions comprising to by weight tris(difluoroamino)fluoromethane are preferred for use with most conventional fuels. Compositions in which the two components are present in substantially a 1:1 molar ratio, that is, where tris(difluoroamino)fluoromethane comprises about 66% to 68% by weight of the composition, are especially useful oxidizers with fuels such as pentaborane or mixtures of unsymmetrical dimethyl hydrazine and hydrazine. However, it has been noted that even in the presence of only trace amounts of dinitrogen tetraoxide, tris(difiuoroamino)fluoromethane is more stable toward thermal and mechanical shock.

Tris(difluoroamino)fluoromethane are miscible at all temperatures above the freezing point of dinitrogen tetraoxide. If nitric oxide is incorporated into the compositions, the components remain in solution.

It is to be understood that the present invention contemplates using nitric oxide in any of the oxidizer compositions in order to lower the freezing point of the solutions.

As previously mentioned, to 15% weight nitric oxide based on the weight of dinitrogen tetraoxide (for example, 5 g. to 15 g. nitric oxide per 100 g. of N 0 will generally be used for this purpose with to 12% usually being employed although greater or lesser amounts can be utilized.

To prepare the oxidizer compositions of the invention, all that is necessary is that the two ingredients be mixed together. Since the boiling point of the ingredients is less than normal room temperature, it is desirable to conduct the mixing of the two liquids at a temperature less than the boiling point of either ingredient. Temperatures of 0 C. to 5 C. are excellent for mixing and storing the oxidizer solution.

The vapor pressure of the oxidizer solutions of the invention fall somewhere between the vapor pressures of the components (see the figure) depending on the concentration of the components. The compositions selected to meet military standards should not have vapor pressures which exceed 500 pounds per square inch at 160 F. The preferred oxidizer composition, that is the composition comprising a 1:1 molar ratio of trisdifluoroamino) fiuoromethan and dinitrogen tetraoxide meets this requirement. It is obvious, however, that for non-military application, the vapor pressure of the oxidizer compositions is of no real concern.

Another advantage of the oxidizer solution is its stability. Cycling a solution of a 1:1 molar ratio of dinitrogen tetraoxide and tris(difluoroamino)fluoromethane (to which has been added about 12% by weight based on weight of N 0, nitric oxide to lower the freezing point) between room temperature and that of liquid nitrogen repeatedly produced no detonations.

An additional advantage of the high-energy oxidizer of the invention is that it produces hypergolic ignitions with many fuels. Hydrazine, unsymmetrical dimethyl hydrazine, mixtures of hydrazine and unsymmetrical dimethyl hydrazine, and pentaborane are examples of the types of fuels which are hypergolic with these oxidizer solutions. Since the oxidizer contains both oxygen and r fluorine, it is useful for the oxidation of a wide variety of rocket fuels. For those fuels which might not undergo hypergolic ignition, conventional igniter devices can be used to initiate combustion.

Two rocket fuels appear to be particularly useful with the present oxidizer compositions. Pentaborane and, as an oxidizer, a solution of a 1:1 molar ratio of tris(difiuoroarnino)fluoromethane and dinitrogen tetraoxide has a theoretical specific impulse of 320 seconds based on a chamber pressure expanded from 1000 pounds per square inch to atmospheric pressure. With the same oxidizer composition, a fuel consisting of a mixture of a 1,875:1 molar ratio of hydrazine and unsymmetrical dimethyl hydrazine has a theoretical specific impulse of 310 seconds expanded from a chamber pressure of 100 pounds per square inch to atmospheric pressure. To achieve such high specific impulses, the oxidizer and fuel should be injected into the combustion chamber so that the molar ratio of pentaborane to tris(difluoroamino)fluoromethane to dinitrogen tetraoxide is about 1:1.7:1.7. With the hydrazine mixture as a fuel, the molar ratio of hydrazine to unsymmetrical dimethyl hydrazine to dinitrogen tetraoxide to tris(difluoroamino)fiuoromethane should be about l.875:1:1.8:1.8.

It will be apparent to those skilled in the art that the ratio of oxidizer to fuel in the combustion chamber will vary depending on the amounts of each of the two components in the oxidizer, the particular fuel, and the particular reaction motor. The determination as to the best ratio oxidizer to be used with a particular fuel in a given motor can be determined after a few static firings of the engine using different ratios. Calculations based on the planned stoichiornetry can also serve as a guide in determining the most desirable ratios.

As the oxidizer of the invention is hypergolic with many conventional liquid fuels, it is especially suitable for use in the operation of liquid bipropellant reaction motors. All that is required to utilize the oxidizer in a liquid bipropellant rocket engine is to simultaneously bring together the oxidizer and the fuel in the combustion chamber. Upon contact, ignition is spontaneous. The ratio of oxidizer to fuel will vary in accordance with the explanation given hereinabove.

The conventional bipropellant reaction motors now in use operate satisfactorily with the high-energy oxidizer of the invention. Storage tanks, injectors, combustion chambers, and nozzles presently utilized are completely acceptable for use with the oxidizer. It is apparent that, as With any given propellant system, certain modifications in the motor design can assist in securing the optimum performance from the oxidizer compositions.

The detailed description presented herein is for purposes of illustration only and no undue limitation should be attributed to the invention as a result thereof except as reflected in the appended claims.

We claim 1. As a high energy liquid oxidizer, a composition consisting essentially of about 20% to 80% by weight tris- (difluoroamino)fiuoromethane, the remainder of the composition being dinitrogen tetraoxide.

2. An oxidizer according to claim 1 wherein nitric oxide is added to the composition in an amount equal to from 5% to by weight based on the weight of dinitrogen tetraoxide in said composition.

3. An oxidizer according to claim 1 wherein tris(difiuoroamino)fiuoromethane is present in an amount of 55% to 75% by weight.

4. As a high energy liquid oxidizer, a composition consisting essentially of about 66% to 68% by weight tris(difiuoroamino)fluoromethane, the remainder of said composition being dinitrogen tetraoxide.

5. An oxidizer according to claim 4 wherein nitric oxide is present in an amount equal to form 5% to '15 by weight based on the weight of dinitrogen tetraoxide in said composition.

6. The method of operating a bipropellant reaction motor which comprises bringing together in the combustion chamber of said motor an oxidizer consisting essentially of about to 80% by weight tris(difluoroamino)fiuoromethane, the remainder of the oxidizer being dinitrogen tetraoxide, and a fuel which is a member selected from the group consisting of unsymmetrical dimethyl hydrazine, an unsymmetrical dimethyl hydrazinedhydrazine mixture and pentaborane.

7. The method according to claim 6 wherein tris- (difluoroamino)fluoromethane comprises about to by weight of said oxidizer.

8. The method according to claim 6 wherein said fuel is pentaborane.

9. The method according to claim 6 wherein said fuel is unsymmetrical dimethyl hydrazine.

10. The method according to claim 6 wherein said fuel is a mixture of unsymmetrical dimethyl hydrazine and hydrazine.

6 11. The method according to claim 10 wherein said 3,345,821 10/1967 Magee 60214 mixture consists essentially of substantially 51 121.875 3,383,859 5/1968 Croomes 60214 ratio of unsymmetrical dimethyl hydrazine and hydrazine.

BENJAMIN R. PADGETT, Primary Examiner References Cited UNITED STATES PATENTS U.S. Cl. X.R.

3.310,444 3/1967 Gould et al. 149-74 14922, 36, 74 

6. THE METHOD OF OPERATING A BIPROPELLANT REACTION MOTOR WHICH COMPRISES BRINGING TOGETHER IN THE COMBUSTION CHAMBER OF SAID MOTOR AN OXIDIZER CONSISTING ESSENTIALLY OF ABOUT 20% TO 80% BY WEIGHT TRIS(DIFLUOROAMINO)FLUOROMETHANE, THE REAMINDER OF THE OXIDIZER BEING DINITROGEN TETRAOXIDE, AND A FUEL WHICH IS A MEMBER SELECTED FROM THE GROUP CONSISTING OF UNSYMMETRICAL DI- 